Free fatty acids and soaps may be present in many different types of fats and oils and generally it is desirable to remove or minimise the concentration thereof.
By the term "crude oil" as used herein we mean any oil that is obtained from seeds or other plant and animal matter. These oils may be produced by any known method. For example they may have been extracted from any known source of oil by any known mechanical or chemical extraction process.
When a crude oil or fat is produced by pressing, extraction, rendering or any other means it contains a variety of non-triglyceride impurities such as free fatty acids (FFA), phosphatides, sterols, pigments and hydrocarbons. Not all of these impurities are undesirable as in some instances they can impart important or preferred characteristics to the final oil product.
It is generally desirable, however, to remove or minimise the content of free fatty acids and soaps in the processed oil. Whilst the level of reduction of free fatty acids in the end product will vary depending on the desired use of the fat or oil, it is generally desirable to reduce the level of free fatty acids to less than 0.2%. Similarly it is generally desirable to reduce the level of soaps to less than 50 parts per million (ppm).
In most instances the free fatty acids are removed by the standard alkali refining process which includes the addition of caustic soda (NaOH) to the crude oil to form a largely oil insoluble sodium based soap which is then separated from the oil.
If soaps are present in an oil or fat they are generally removed by water washing to reduce the soap concentration to about 50 ppm then reduced further by treatment with a suitable bleaching earth or other adsorbent material.
The advantages of using caustic soda to remove free fatty acids include that it is readily available and it may also assist with the removal of other impurities such as phosphatides, carbohydrates and protein fragments. Further, it has been found that large quantities of oil can be refined with a high efficiency and minimum attention after the selection of: (a) preferred or optimum selection of the best method of separating the soap from the oil and (b) the optimum quantity and concentration of caustic soda.
The disadvantages of using caustic soda include that in general it is necessary to use a multi-step process to remove all the impurities and to handle the caustic materials. Further such an oil refining process produces a soap stock which is not environmentally friendly and requires further processing prior to disposal. Historically the soap stock was used in traditional soap processes, however, its disposal this way has decreased over recent years due to the greater use of detergents in preference to soaps. One solution for overcoming the disposal problem has been to further process the soap stock by acidulation to form free fatty acids which may be used as a high-energy ingredient in animal feeds or for chemical use. However, these further processes can be expensive and usually involve the use of other undesirable chemicals.
Attempts to effectively refine oils with other alkali materials such as calcium hydroxide and sodium carbonate have been tried. However, these compounds have not been proven to be as satisfactory as caustic soda and their use has been either abandoned or curtailed. For example, calcium hydroxide added as a "cream" to a crude oil requires several hours to reduce the FFA to about 0.2%. Sodium carbonate, on the other hand, does not possess the decolourising capacity of caustic soda but saponifies very little neutral oil.
It is also desirable in some instances to remove free fatty acids and/or soaps from, or minimise them in, fats and oils where the level of said free fatty acids or soaps have increased due to one or more chemical reactions such as during hydrogenation or esterification or frying. For example, the interest-erification of fats and oils may use an alkaline compound, notably sodium methoxide, to effect the randomisation. Water added at the completion of the reaction causes soap to be formed, these being usually removed by acidification and/or water washing.
In Russian Patent No. SU207310 it is reported that it is known to neutralise vegetable oils by treating them with magnesium oxide. This document teaches that this process can be improved by adding a dehydration agent to the oil with the magnesium oxide. The dehydration agent disclosed in this document is gypsum. However, this process has not been widely used and it does not result in the removal of the free fatty acids to commercially acceptable levels. This document also does not suggest or teach that any other alkali metal oxide could be used in an oil or fat refining process.
It is an object of the present invention to develop a method for refining oils and fats to reduce the level of free fatty acids or soaps from the oils or fats in an economical and environmentally friendly way.